An otoscope is a portable, direct viewing examination instrument that aids in the observance and study of the inner ear canal, including the tympanic membrane. Many otoscopes are presently known, each typically having a housing including a frusto-conical head portion and specula capable of being placed a predetermined distance within the ear canal of a patient. The interior of the housing includes an optical viewing system, as well as an illumination system for providing light in a coaxial manner with the viewing system. In use, the optics permit viewing using an eyepiece attached to a proximal end of the housing.
With the advent of "telemedicine", videoized versions of medical examination instruments, including otoscopes, have been developed, such as those described in U.S. Pat. No. 5,363,829 issued to Lankford; U.S. Pat. No. 5,239,984, issued to Cane, et al; and U.S. Pat. No. 4,947,245, issued to Ogawa, et al. In each of the above, a miniature video camera, such as a CCD or other electronic sensor, is positioned either within the interior of the instrument or adjacently coupled thereto. The electronic sensor includes a light receiving surface or substrate which receives a focused optical image of a target of interest through the optical viewing system. The sensor then converts the optical signal into an electrical signal and subsequently through processing electronics into a monitor-ready video signal.
In order to provide a complete ear examination of a patient, it is desirable that the otoscope include the capability of producing a stream of air for stimulating the tympanic membrane. This feature is known as insufflation.
To provide insufflation capability, the inner tip housing of the otoscope must be sufficiently large enough to accommodate the illumination system, the optical viewing system, and an air path permitting insufflation.
In addition, and though the ear canal is a relatively small chamber, it is also desirable to provide a sufficient field of view to allow the entirety of the tympanic membrane (approximately 8 mm) to be viewed at one time during an examination. In the past, videoized versions of otoscopes have utilized relay lens systems to achieve this goal.
Several attempts to attach a video camera to a standard otoscope have proved less than successful due to compromises in field size, vignetting (clipping) and lack of video lens interchangeability. In addition, the lens elements must be under three millimeters in diameter in order to fit inside the specula tip of the otoscope.
In order to achieve the relatively long total conjugate length (approximately 99 mm) of a video otoscope, While maintaining the small element diameters (under 3 mm) required, the resulting optical system tends to be complex. Most of these lens systems 126 are composed of some form of objective means in the distal portion 122 of the otoscope, followed by one or more relay configurations. This type of system has many disadvantages based upon to its overall complexity, therefore producing greater likelihood of manufacturing errors, and requiring a plurality of intermediate imaging planes 138, as shown in FIG. 1. The intermediate image planes 138 are necessitated by the relay configurations and are subject to cosmetic issues.
As shown in FIG. 1, these known lens systems include a number of axially disposed optical elements which transmit the optical signal through a series of intermediate image planes located between the target plane 140 and the image substrate 134 of a miniature video camera along an axis 130.
For a normally constructed objective lens system, the object and image plane conjugates are essentially in proportion to the system magnification, or more specifically to the ratio of M and 1/M, in which M is the system magnification. By knowing the desired magnification, (1:1), (1:2), etc., it is straight forward to calculate the total conjugate length (the distance from the object to image) for any focal length. Similarly, the focal length required to achieve a desired total conjugate length is also easily calculated.
It is readily known that an objective lens system operating at unit magnification (1:1) is normally located equidistant from the object and image planes. For an objective lens system to operate at a reduction of 0.5 (1:2), the object conjugate must normally be twice that of the image conjugate.
Most often undesirable or unattainable objective positions are produced with the lens systems typically employed in many videoized instruments, including otoscopes. It is desirable to produce a system that allows for the placement of the objective lens at a more favorable location.